Motion control systems are well-known in the art. In many applications, it is necessary to position a movable component with precision and repeatability. One type of motion control system utilizes an encoder strip that is optically scanned by sensors on the movable component.
Inkjet printing systems are also are well-known in the art. Small droplets of liquid ink, propelled by thermal heating, piezoelectric actuators, or some other mechanism, are deposited by a printhead on a print media, such as paper.
In scanning-carriage inkjet printing systems, inkjet printheads are typically mounted on a carriage that is moved back and forth across the print media. As the printheads are moved across the print media, the printheads are activated to deposit or eject ink droplets onto the print media to form text and images. The print media is generally held substantially stationary while the printheads complete a “print swath”, typically an inch or less in height; the print media is then advanced between print swaths. The need to complete numerous carriage passes back and forth across a page has meant that inkjet printers have typically been significantly slower than some other forms of printers, such as laser printers, which can essentially produce a page-wide image.
The ink ejection mechanisms of inkjet printheads are typically manufactured in a manner similar to the manufacture of semiconductor integrated circuits. The print swath for a printhead is thus typically limited by the difficulty in producing very large semiconductor chips or “die”. Consequently, to produce printheads with wider print swaths, other approaches are used, such as configuring multiple printhead dies in a printhead module, such as a “page wide array”. Print swaths spanning an entire page width, or a substantial portion of a page width, can allow inkjet printers to compete with laser printers in print speed.
One type of inkjet printing system utilizes multiple printhead modules that each print a substantial portion of a page width; the modules are on carriages that must be accurately positioned such that visible print defects are not introduced where the separately-printed portions of the page meet. The carriages may also be repositioned during the printing process, such as to allow wider page sizes to be printed using multiple print passes.
Printing is a highly-competitive field, and motion control techniques that may be appropriate in industrial applications are often not cost effective in a printing system. Lower cost materials may also be employed in a printing system; these materials may be more susceptible to environmental effects such as heat and humidity.
There is thus a need for apparatus and methods that allow for the precise and repeatable positioning of movable components at a reasonable cost.